Why A 100 watt HF transceiver draws roughly 20 to 25 amps on transmit peaks (about 100 W output plus losses at around 13.8 V). Auxiliary or cigarette-lighter sockets are typically fused at 10 to 15 amps and use light gauge wire with a loose plug contact, so the wiring can overheat and the voltage sags badly under key-down. The recommended practice is a heavy gauge fused cable run directly to the battery terminals.